Fault Code P0446 - EVAP(Evaporative Emission System) purge/vent solenoid circuit condition. Your Toyota Camry EVAP system has a pressure sensor to detect if the tank remains pressurized while the EVAP monitor is running, basically insuring it is not leaking. If the tank depressurizes during the EVAP test, a trouble code(s) is set indicating a vapor leak and/or a defective EVAP system component(s).
1.) Purge or vent solenoids defective
2.)Check connector and wiring
3.)Fuel saturated vapor canister
4.)Failed EVAP vent solenoid
Initially check all hoses to the charcoal canister and VSV systems. Your Toyota's charcoal canister could have a leak, defective VSV for pressure sensor or vapor pressure sensor. Purchase a new Charcoal Canister. It will be equipped with a new Pressure Sensor and Vent Valve.